This invention relates to safely packaging low-level radioactive waste materials for disposal in the ocean, and more specifically, to providing a packaging system that has a life expectancy which will exceed the length of time (over 100 years) necessary for the low-level radioactive way to decompose or radiodecay to environmentally innocuous materials.
Present methods for ocean disposal of low-level radioactive wastes use 55 gallon steel drums which are either pressure-compensated or monolithic (solid). Typically the drums are of the monolithic type by being tightly sealed after filling with a matrix. The matrix is either an asphaltic (bitumen) material mixed with about an equal volume of solid radioactive waste material or a cement/sand mixture combined with waste in an approximate ratio of 3 to 1 parts by volume.
The drums are transported to the ocean dump site and discharged by free falling to the seafloor.
An onsite inspection of drums containing a cement matrix 22 years after disposal at 1,000 m water depth showed that the most common mode of failure was crushing of the drums because the strength of the matrix was not sufficient to withstand the pressure loads from the ocean environment. Corrosion of steel was evident; however, breached drums showed more distress from corrosion because attack occurred both internally and externally.
The European Community presently uses an asphalt matrix which provides good support to the drum in resisting collapse. However, the corrosion problem of the steel still exists.
Other systems adapted for burial on land use containers for holding a plurality of standard steel drums with foamed polyurethane surrounding and occupying the spaces between drums. This system, however, is unsuitable for deep ocean disposal because of ease in rupture of the container and foam.
Mixing radioactive wastes with dry cement in a canister, alone, where a breach in the canister will permit entry of water from a storage tank to form a concrete patch against leakage of wastes will not work satisfactorily at deep ocean depths due to high pressure leaks, buckling, and exposure of wastes to the biosphere.
The state of art at present needs improvement because 55-gallon drums do not offer a safe barrier in isolating radioactivity from the environment. It is estimated that for the low-level waste, a sufficient barrier system should contain the radioactive material for ten half-lives. This places a requirement on the packaging method for a life of 100 to 200 years.